Polyphenol Oxidase Activity on Guaiacyl and Syringyl Lignin Units
The natural heterogeneity of guaiacyl (G) and syringyl (S) compounds resulting from lignin processing hampers their direct use as plant-based chemicals and materials. Herein, we explore six short polyphenol oxidases (PPOs) from lignocellulose-degrading ascomycetes for their capacity to react with G-...
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Published in | Angewandte Chemie International Edition p. e202409324 |
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Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
17.09.2024
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Online Access | Get full text |
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Summary: | The natural heterogeneity of guaiacyl (G) and syringyl (S) compounds resulting from lignin processing hampers their direct use as plant-based chemicals and materials. Herein, we explore six short polyphenol oxidases (PPOs) from lignocellulose-degrading ascomycetes for their capacity to react with G-type and S-type phenolic compounds. All six PPOs catalyze the ortho-hydroxylation of G-type compounds (guaiacol, vanillic acid, and ferulic acid), forming the corresponding methoxy-ortho-diphenols. Remarkably, a subset of these PPOs is also active towards S-compounds (syringol, syringic acid, and sinapic acid) resulting in identical methoxy-ortho-diphenols. Assays with 18O2 demonstrate that these PPOs in particular catalyze ortho-hydroxylation and ortho-demethoxylation of S-compounds and generate methanol as a co-product. Notably, oxidative (ortho-)demethoxylation of S-compounds is a novel reaction for PPOs, which we propose occurs via a distinct reaction mechanism compared to aryl-O-demethylases. We further show that addition of a reducing agent can steer the PPO reaction to form methoxy-ortho-diphenols from both G- and S-type substrates rather than reactive quinones that lead to unfavorable polymerization. Application of PPOs opens for new routes to reduce the heterogeneity and methoxylation degree of mixtures of G and S lignin-derived compounds.The natural heterogeneity of guaiacyl (G) and syringyl (S) compounds resulting from lignin processing hampers their direct use as plant-based chemicals and materials. Herein, we explore six short polyphenol oxidases (PPOs) from lignocellulose-degrading ascomycetes for their capacity to react with G-type and S-type phenolic compounds. All six PPOs catalyze the ortho-hydroxylation of G-type compounds (guaiacol, vanillic acid, and ferulic acid), forming the corresponding methoxy-ortho-diphenols. Remarkably, a subset of these PPOs is also active towards S-compounds (syringol, syringic acid, and sinapic acid) resulting in identical methoxy-ortho-diphenols. Assays with 18O2 demonstrate that these PPOs in particular catalyze ortho-hydroxylation and ortho-demethoxylation of S-compounds and generate methanol as a co-product. Notably, oxidative (ortho-)demethoxylation of S-compounds is a novel reaction for PPOs, which we propose occurs via a distinct reaction mechanism compared to aryl-O-demethylases. We further show that addition of a reducing agent can steer the PPO reaction to form methoxy-ortho-diphenols from both G- and S-type substrates rather than reactive quinones that lead to unfavorable polymerization. Application of PPOs opens for new routes to reduce the heterogeneity and methoxylation degree of mixtures of G and S lignin-derived compounds. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 content type line 23 ObjectType-Feature-2 |
ISSN: | 1521-3773 1521-3773 |
DOI: | 10.1002/anie.202409324 |